Service providers and device manufacturers are continually challenged to deliver value and convenience to consumers by, for example, providing compelling print management administrative services. Image non-uniformity has long been a difficult problem for most digital marking processes. Such non-uniformity can occur across an image printed by a single printing device, or may be prevalent among images printed by any or all printing devices among a group of printing devices. Image non-uniformity can take many forms such as, for example, streaks, bands, and/or variations in gray level in the printed image. It is to be appreciated, however, that the defects discussed are only exemplary, and embodiments described herein are not limited to defects running parallel to a process direction.
Conventional spatial uniformity correction via spatially varying tone reproduction curves (sTRCs) and spatially varying multi-dimensional lookup tables (sDLUTs) has been demonstrated to be effective in compensating for monochromatic and process-color streaks, and in compensating for side-to-side non-uniformity. These methods generally map a set of spatially varying engine response curves across a page to a mean engine response to attain a spatially uniform overall printer response.
However, conventional spatial non-uniformity correction techniques often fail to achieve a mean density for all positions on the page for densities close to the maximum density (Dmax). A similar problem exists for process-color streaks and sDLUTs. That is to say, the spatial mean color gamut may be unattainable by some of the local engine responses, thus rendering the compensation ineffective for particular colors on certain portions of the page. In other words, if a spatial mean color gamut is determined, all printing systems among a group of printing systems may not be able to achieve all of the colors within the spatial mean color gamut. As such, conventional spatial uniformity correction techniques may only compensate for non-uniform image defects for a one or more printers locally, but fail to correct spatial non-uniformity among all printing systems in a group.
Conventional sDLUT implementations for streak compensation map the local engine response to the spatially averaged engine response. This method suffers from a limitation in its ability to compensate for streaks because the color gamut defined by this mean engine response may be unattainable at portions of the page where the local engine response curves have smaller color gamuts, for example. Accordingly, streak compensation will not be effective for out-of-gamut colors at those regions.